Apparatus and method for reducing speckle in display of images

ABSTRACT

An apparatus and method of reducing speckle in projection of images is provided that includes the elements or features of producing a first image and displacing the first image to produce a second image that will reduce speckle relating to the first image when the first image and the second image are displayed on a display medium.

This application is a divisional of application Ser. No. 11/618,401,filed Dec. 29, 2006.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The disclosure herein relates generally to an apparatus and a method fordisplaying images.

2. Background Information

Spatial light modulators, which typically perform a form ofspatial-variation on a property of a beam of light, such as its phase,intensity, etc., are used in sequential color display systems to projectimages for various video media sources such as High DefinitionTelevision (HDTV), Digital Video Disc (DVD) players, and Digital VisualInterface (DVI) devices. Viewers generally evaluate display systemsbased on criteria such as image size, resolution, contrast ratio, colorpurity, and brightness. Image brightness is a useful metric because theavailable brightness can limit the size of the projected image andbecause it can also control how well the image can be seen in highlevels of ambient light. The brightness of a given projection display issometimes increased by increasing the size of the light source used toform the image. However, increasing the size of the light source alsoincreases the cost, size, and weight of the entire display system.Additionally, larger light sources generate undesirable additional heat.

Another approach to increasing the brightness at the display has been touse an inherently brighter light source, such as a laser. However, theuse of laser illumination in projection display systems often results ina substantially random spatial intensity modulation known as “speckle.”Speckle arises when viewing a coherent light, such as laser light, on ascreen which is rough compared to the wavelength of the coherent light.The term “rough” typically means a surface whose local irregularities indepth are greater than one quarter of the wavelength of the coherentlight. The appearance of speckle can vary as a viewer's head moves inrelation to the screen, which can make the appearance of speckle evenmore objectionable. Thus, there is a need for a projection displaysystem that can reduce speckle.

SUMMARY OF THE PRESENT DISCLOSURE

In one aspect, a method for producing an image is disclosed thatincludes producing a first image, displacing the first image in aselected direction to produce a second image that will reduce specklerelating to the first image when the first and second images aredisplayed on a display medium.

In another aspect, an apparatus for producing images for displaying on adisplay or projection medium is disclosed that may include a laser thatproduces light, a modulator that produces a plurality of images, and anoptical element between the laser and the display medium for displacingthe plurality of images so as to reduce speckle associated with theprojection of the plurality of images on the projection medium.

Only certain exemplary features of the invention are summarized hereinrather broadly in order that the detailed description thereof thatfollows may be better understood and in order that the contributions tothe art may be appreciated. There are, of course, additional features ofapparatus and method for reducing speckle in display images that aredescribed hereinafter and which form the subject of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures form part of the present disclosure and areincluded to further demonstrate certain aspects of the claimed subjectmatter and should not be used to limit the claimed subject matter. Theclaimed subject matter may be better understood by reference to one ormore of these drawings in combination with the description of drawingspresented herein. Consequently, a more complete understanding of theembodiments and further features and advantages thereof may be acquiredby referring to the following description taken in conjunction with theaccompanying drawings, in which like elements are generally identifiedby like reference numerals, wherein:

FIG. 1 schematically illustrates an exemplary projection display systemusable to reduce speckle in the display of laser-illuminated images;

FIG. 2 schematically illustrates an isometric view of an exemplaryembodiment of a projection display system that includes a specklereduction feature of FIG. 1;

FIG. 3 schematically illustrates an exemplary spatial light modulatorsuitable for use in the projection display systems of FIGS. 1 and 2 forproducing images;

FIG. 4 schematically illustrates an exemplary pixel field produced usingthe exemplary spatial light modulators of FIG. 3 and the effect ofdisplacing or shifting a particular pixel;

FIG. 5 schematically illustrates another exemplary pixel field producedby the spatial light modulator of FIG. 3 and the effect of displacing orshifting a set of pixels; and

FIG. 6 illustrates a flowchart of an exemplary method for reducingvisible speckle in a laser-illuminated projection display system,according to one aspect of the disclosure.

It is to be noted, that the appended drawings illustrate only typicalembodiments of the claimed subject matter and are, therefore, not to beconsidered limiting the scope of the claimed subject matter.

DETAILED DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the claimed subject matter are described indetail below. In the interest of clarity, not all features of an actualimplementation are described in this specification. It will of course beappreciated that numerous implementation-specific changes andmodifications will be apparent to one skilled in the art upon having thebenefit of this disclosure and which changes and modifications may varyfrom one embodiment to another and may be made without departing fromthe scope of the claimed subject matter.

FIG. 1 schematically illustrates an exemplary embodiment orconfiguration of a projection system 100 (also referred to as theprojection display system) for reducing speckle relating to the displayof images on a display medium. In one aspect, the projection system 100produces at its output a beam of light 125 a for projection onto asuitable display or projection medium 140. The display medium 140 may beany suitable medium, including but not limited to a flexible or rigidsurface that has diffusive properties in transmission or scatteringproperties in reflection. The display medium may be a rear-projectionscreen or a front-projection screen or another surface, such as a paper,fabric, wall, plastic and the like. The projection system 100 includes alight display system 102 that may house certain image-producingcomponents of the light projection system 100, including: anilluminator, such as laser 105 (also referred to as a laser illuminator)for producing visible light (e.g. light of primary colors red, blue, andgreen) that is generally used for image formation in projection displaysystems; and a light modulator 110, such as a digital micromirror device(DMD) for converting a light beam 120 from the laser illuminator 105into individual pixels which form an image at the display medium 140.The modulator 110 may include an array of individual micromirrors thatdigitally operate to reflect individual pixels corresponding to thelight beam. Digital micromirror devices and other modulators are knownin the art and are thus not described in detail herein. Any othersuitable modulator may also be used for the purpose of this disclosure.

The light display system 102 also includes an image-displacement device(also referred to as the displacement device), such as a device 130 a,and a projection lens module or system 150. The projection lens system150 may include one or more rear-end lenses 152 and one or morefront-end lenses 154. The image-displacement device 130 a, in one modeallows the light beam 122 to pass in the direction delivered by themodulator 110 as shown by beam 125 a. In another mode, theimage-displacement device shifts or displaces the light beam 122 by aselected amount along a selected direction as shown by light beam 125 b.

In FIG. 1, the light beam 125 b is shown shifted from the initial beam125 a by a distance defined by gap 127 along a particular direction. Theoriginal beam 125 a and the displaced beam 125 b produce images 128 aand 128 b on the display medium 140 respectively. The image-displacementdevice 130 a may be moved in any desired direction so as to be able todisplace the received images, such as images in the beam 122, by adesired amount in a desired direction and at a desired frequency. Anysuitable actuator (device or mechanism) 132 a may be used to cause thedisplacement device 130 a to move to displace the received images. Inone aspect, the actuator 132 a may be a piezoelectric element or devicethat can be actuated to periodically move the image-displacement device130 a by any suitable amount in any suitable direction and at anysuitable frequency. Thus, the image-displacement device 132 a canoptically dither the received images by a selected amount in a selecteddirection and at a selected frequency.

In one aspect, the image-displacement device 130 a may be placed alongthe path of beam 122 and between the modulator 110 and the projectionlens system or block 150 as shown by element 130 a. In another aspect,the image-displacement device may be placed within the projection lenssystem or block 150, such as shown by the image displacement device 130b. FIG. 1 shows the image-displacement device 130 b placed between therear-end lenses 152 and front-end lenses 154. The image-displacementdevice 130 a or 130 b may, however, be placed or positioned at any othersuitable location within the projection system 100, including betweenthe projection lens 154 and the display medium 140. Theimage-displacement device 130 a may be any suitable optical element ordevice, including but not limited to one or more lenses, one or moremirrors, a transmissive plate with parallel faces or surfaces or anoptical element having non-parallel faces or surfaces (such as wedges),one or more prisms, etc. When mirrors are used as theimages-displacement device, the incident light beam strikes the mirrorsat a selected angle that is deflected by the mirrors. The mirrors may bemoved by an actuator to obtain the desired displacement of the receivedimages.

The projection system 100 may further include a controller 160 forcontrolling the operation of various elements of the light displaysystem 102. In one aspect, the controller 160 may include a processor,such as a microprocessor, and may have an associated memory 162 forstoring data and computer programs 164 that provide programmedinstructions to the processor 160 for controlling the operation of oneor more elements of the projection system 100. In one aspect, thecontroller 160 provides signals to the actuator 132 a or 132 b thatcontrol the movement of the image-displacement device 130 a or 130 b. Inanother aspect, the controller 160 may also be used to control theoperation of the modulator 110. The controller 160 may select theoperating parameters, such as the amount, direction and frequency ofoperation of the displacement device 130 a or 130 b from a look-up tableor according to algorithms and instructions contained in the programs164. In one aspect, the controller 160 may select one or more suchparameters based on a throw ratio or distance between theimage-displacement device 130 a or 130 b and the display medium 140 orany other suitable criterion.

The laser 105 may be any suitable light source, including but notlimited to, light-emitting diodes, super-luminescent diodes, solid-statelasers, gas lasers, liquid lasers, diode-pumped solid-state lasers,direction-emission diodes, and the like. In one aspect, the laser 105 isa coherent light source that may include one or more lasers. In oneaspect, the light beam 120 may include more than one beam, for example,three beams of light, generally at wavelengths representative of red,green, and blue light. In one aspect, each color of light may beproduced by an individual laser source.

In operation, the modulator 110, in one aspect, may produce a series ofsequential images or frames at a selected frequency, for example afrequency between 20 Hz and 60 Hz. The controller at a first instance oftime allows the displacement device to pass the image without displacingthe image and a fraction of time later (i.e., at a second instance oftime or later time) moves the image-displacement device by a selectedamount in a selected direction, which produces a displaced imagecorresponding to the original image. The displaced image passes to thelens block 150 a fraction of time later than the original image. In thismanner the original image, such as image 125 a is first displayed on thedisplay medium 140 and the displaced image 125 b corresponding to theoriginal image 125 a is displayed a fraction of time thereafter. In oneaspect, each image or frame may be displaced in the sequence receivedand projected in the received order. The time between successive imagesor frames is referred to as a frame time. Therefore, in the examplediscussed, each image is displaced within a frame time so that thedisplaced image is projected after projecting its corresponding imagebut before the arrival of the next image. The frequency of the displacedimages may be the same as the frequency of the original images receivedby the displacement device. Images may be displaced by the same amount,such as about one pixel length or less, or by different amounts and inthe same or different directions. The direction may be horizontal,vertical, rotational, or at any selected angle of a two dimensionaldisplay medium, such a screen, CRT or LCD, etc.

FIG. 2 shows an exemplary light projection system 200 (also referredherein as a “projector”) usable to project a spatially modulated lightbeam as described in the present disclosure. The light projection system200 includes a coherent light source such as a laser illuminator 205.The light projection system 200 includes one or more light collection,integration, and/or etendue-matching optical elements 220 arranged tocollect and/or to integrate spatially light emitted by the light source205. Etendue, as one skilled in the art and having the benefit of thepresent disclosure would know, is the product of the area of emissionand the solid angle into which the emission is emitted. The lightprojection system 200 may also optionally include a telecentric relay230 using one or more aspherical refractive and/or reflective components(not shown), and/or a pupil (not shown) for controlling stray light. Theprojector 200 may also optionally include an illumination wedge prism240 to direct a light beam such as beam 225 towards an optical element.The projector 200 also includes a spatial light modulator (SLM) 210,such as the digital micromirror device (DMD), arranged to modulatespatially substantially the light 225 projected onto it. The projectormay also include a projection total internal reflection (TIR) prism 260disposed between the illumination wedge prism 240 and the DMD 210. Inone aspect, the TIR prism 260 may be separated by an air gap (not shown)from the illumination wedge prism 240. The projector 200 may alsoinclude a projection lens 270 for projecting the output beam onto adisplay screen. The image-displacement device (130 a or 130 b), actuator(130 a or 130 b), and controller 160 shown in FIG. 1 may be placedwithin the projector 200 at any suitable location as described inreference to FIG. 1.

The telecentric relay 230 can provide substantially all the lightemitted by the laser illuminator 205 through the illumination wedgeprism 240 and through the projection total internal reflection (TIR)prism 260 to the DMD 210. The DMD reflects and spatially modulates light225 back through the TIR prism 260 that internally reflects thespatially modulated light 220 through the projection lens 270 and onto aprojection display screen, such as screen 140 (FIG. 1).

FIG. 3 shows a schematic illustration of an exemplary spatial lightmodulator (SLM) 300 suitable for use with the present disclosure. FIG. 3shows, in particular, a top perspective view of an SLM 300 usable withan integrated circuit, such as the micro-electro-mechanical system(MEMS) spatial light modulator (SLM) integrated circuit. The SLM 300 hasa wafer level package (WLP) DMD chip 315 bonded thereon. One of ordinaryskill in the art having the benefit of the present disclosure wouldappreciate that the device 300 could be used with any suitableintegrated circuit, including the MEMS SLM integrated circuit describedherein. In one aspect, the device 300 may have the DMD chip 315wire-bonded on two sides to bond pad area 320. The device 300 may alsohave one or more primary datum (‘A’) alignment features 340, one or moresecondary datum (‘B’) alignment features 350, and one or more tertiarydatum (‘C’) alignment features 360 disposed on the top surface 330. Inone embodiment, the SLM may be actuated to orient a light beam at afrequency consistent to provide an image of a single frame at a displayscreen. Each micromirror of the SLM is actuated according to a selectedprogram. In one aspect, a micromirror may be actuated in response to anelectric current passing through a piezoelectric material attached tothe micromirror.

FIG. 4 shows an exemplary field of pixels as viewed at a display screenin one aspect of the present disclosure. The illustrative field includesa plurality of pixels arranged along a grid 400 oriented at an angle toa coordinate system 405. Each pixel is further characterized by a colorcode associated with the pixel. As shown schematically in FIG. 4, eachone of the plurality of the pixels 410 may be represented by arespective bit value R_(i), G_(j), B_(k), where the bit values R_(i),G_(j,) B_(k) may correspond to a suitable “gray scale” encoding of theappropriate red, green, and blue components of the digitally encodedimage, such as R_(i)≡2^(i) R, G_(j)≡2^(j) G, B_(k)≡2^(k) B, where R, G,B are respective elemental (or base) bit values for the red, green, andblue components of the digitally encoded image. Although the illustratedpixels are squares, the pixel is not restricted to a particular shape.Also, the rotational orientation of the grid and pixels therein may bearbitrarily selected.

In accordance with the present disclosure, a pixel may be displaced byan amount selected to reduce speckle. In one aspect the image isdisplaced at least ¼ pixel and at most 1 pixel. A typical displacementmay be about ½ pixel as shown through the displacement of pixel 410 to apixel location 420 through displacement vector 415. The reduction of thevisible speckle from the projection display screen 140 may be producedby the substantially incoherent addition of phasors. This substantiallyincoherent addition of phasors may be produced by projecting pixel 410and displaced pixel 415 within a time frame that is shorter than thereflex time of the human eye. In one aspect, the pixel may be displacedalong a horizontal axis or along a vertical axis or a linear vectorcombination of both horizontal and vertical displacement. FIG. 4illustrates the displacement of one pixel against a grid of pixels. Inoperation, typically a plurality of the pixels, such as the pixels ofgrid 400, are displaced simultaneously along the direction of thedisplacement vector 415.

In one aspect, the actuator 130 a or 132 b (FIG. 1) displaces the outputbeam substantially within about a frame time of the light display system102. For example, if there are about 60 frames per second, then thecorresponding frame time of the projection system is about 1/60 sec=16⅔millisec. The image displacement (also referred to herein as“dithering”) may be done relatively quickly as compared to the temporalresponse of the eye, which may be about the duration of a single frametime or longer.

FIG. 5 schematically illustrates an exemplary pixel field 500 producedat a display medium and the effect of displacing or shifting a set ofpixels. The original pixel field 500 produced by the laser illuminatoris shown to include a set of arbitrary pixels (as an example forillustration purposes only), including pixels designated as G5, G6, G5(green), B5, B8, B9 (blue) and R8, R3, R9 (red). In this example all ofthe pixels in the set 510 are shown oriented in an angular direction of45 degrees relative to an x-y plane 405. The oriented set of pixels isshown by dotted set 520. The set 510 may be displaced in any otherdirection by any desired amount. The set 520 is produced a fraction oftime subsequent to the production of set 510 and each set is displayedon the projection medium in the order produced.

FIG. 6 shows a flowchart of an exemplary method 600 of reducing specklein a projection display. The method 600 includes using laserillumination to produce an image to be displayed at the projectiondisplay, as indicated at box 610. The method 600 also includesdisplacing at least a portion of the image in at least one direction byan amount arranged to reduce the visible speckle at the projectiondisplay, as indicated at box 620. The method 600 also includesdisplaying the image and the displaced image sequentially on theprojection display, as indicated at box 630.

The method 600 may further include displacing a pixel by at most onepixel length and may include displacing a pixel by at least ¼ of a pixellength. The method may further include displacing a pixel within a timeframe which maximizes speckle reduction, typically a frequency withinthe range of 30 Hz to 60 Hz. In another aspect, the image may bedisplaced from between a quarter pixel and 1 pixel within one frametime. In one aspect, an actuator is used to displace the pixelperiodically. In another aspect, a prior image is used and shown at boththe non-displaced pixel and the displaced pixel. The pixel may bedisplaced along an x-axis or y-axis or along a vector defined by alinear combination of x- and y-displacements. In another aspect, aproper subset of the pixel that form an image may be displaced.

Thus, in one aspect, the disclosure herein provides a method forreducing speckle in display images. The method includes producing afirst image using laser illumination for displaying on a display medium;and producing a second image that includes at least a portion of thefirst image, wherein the second image is physically displaced from thefirst image by a selected amount in a selected direction so as to reducevisible speckle relating to the projection of the first image on thedisplay medium. In one aspect, the second image may be produced within aframe time after producing the first image. The physical displacement ofthe second image from the first image may be any desired amount, such asbetween a quarter of a pixel to one pixel of the first image. Thedisplacement direction may be any suitable direction, including, but notlimited to (i) a horizontal direction; (ii) a vertical direction; (iii)at a linear combination of horizontal and vertical directions; or (iv)an angular direction.

In another aspect, the method may comprise: producing a first pluralityof images using a laser-illuminator for sequential projection of thefirst plurality of images onto a display medium; and producing a secondplurality of images, wherein each image in the second plurality ofimages corresponds to an image in the first plurality of images, andwherein each image in the second plurality of images is displacedrelative to its corresponding image in the first plurality of images soas to reduce speckle relating to projection of the first plurality ofimages onto the display medium. In one aspect, the method provides forproducing the second plurality of images in a manner that includes oneof: (i) a displacement of less than one pixel; (ii) a displacement in adirection that is one of horizontal, vertical, a linear combination ofhorizontal and vertical; or at an angle relative to the direction of thefirst plurality of images; (iii) producing each displaced image within aframe time; and/or (iv) at a frequency that is about the same as that ofthe frequency of the first plurality of images.

In another aspect, some of the images in the first plurality of imagesmay be displaced. Any displaced image may include all or a portion of animage or a frame. The method further provides for producing the secondplurality of images by controllably moving an optical element betweenthe laser-illuminator and the display medium. The optical element may beplaced: (i) between a modulator and a projection lens; or (ii) within aprojection lens block that includes at least one lens that is adapted toproject the first and second plurality of images onto the displaymedium. One or more computer programs stored in a memory orcomputer-readable medium associated with the controller includeinstructions that are executed by the controller to perform the variousaspects, features or steps of the methods provided herein. The methodmay further provide for selecting the frequency of the second pluralityof images based on one of: (i) a throw ratio; and (ii) a distancebetween an optical element in a laser illumination system that displacesthe first plurality of images and the image display medium. The firstplurality of images and the second plurality of images may be projectedsequentially at a selected frequency wherein the images in the secondplurality of images are projected within frame time of theircorresponding images in the first plurality of images.

In another aspect, the disclosure provides an apparatus for producingimages for displaying on a projection medium that includes a laserilluminator that produces a plurality of images in a first timesequence; a lens that projects the plurality of images onto a projectionmedium; and an optical element between the laser-illuminator and thelens for selectively displacing the first plurality of images so as toreduce speckle associated with the plurality of images on the projectionmedium. The optical element may be any suitable device that can displacethe images, such as a lens or a mirror. An actuator, such as apiezoelectric element, may be used to move the optical element. Acontroller that may include a processor may be used to control theoptical element to displace or shift the images in the plurality ofimages by an amount that is at least one of: (i) less than one pixel ofan image in the plurality of images; (ii) in a direction that is one ofhorizontal, vertical, a linear combination of horizontal and vertical,at an angle relative to the first plurality of images; (iii) at afrequency that is the same as that of the first plurality of images; and(iv) with a time difference of less than a frame. The optical elementmay be placed at any suitable location within the apparatus, includingbetween the laser illuminator and a projection lens that projects theimages, within a lens block that includes one or more projection lenses,or between a projection lens and the display medium. The controller mayselect the frequency for displacing or shifting the images in theplurality of images based on one of: (i) a throw ratio; (ii) distance ofan optical element that shifts the images in the plurality of images andthe display medium. The apparatus may further include a light source anda micromirror device for generating the plurality of images.

In another aspect, an image projection system is disclosed that includesa laser-illuminator that produces a plurality of light beamssequentially; a modulator that produces a plurality of images using theplurality of light beams; an actuator that displaces the plurality ofimages by a selected amount in a selected direction to reduce speckleassociated with the projection of the plurality of images on the displaymedium. The display medium may be one of (i) a cathode ray tube; (ii) aliquid crystal display; or (iii) a flexible screen.

Each apparatus made and method practiced according to the disclosure canbe useful for reducing visible speckle in a laser illuminated projectiondisplay and may be advantageous in providing an improved approach to theuse of inherently brighter light sources, such as ones using laseremissions. The terms image displacement, shifting and image ditheringare used synonymously. In each case, the image displacement may berelatively small, for example one pixel or less, in either or bothdimensions. The image displacement or dithering may be done relativelyrapidly compared with the temporal response of the human eye which isgenerally within a frame time for digital display. An optical element ordevice, such as a lens or a scanning mirror is selectively controlled todisplace the images. The displacement of the images may be done withoutprior image processing or with prior image processing. The images can becontinuously or discretely dithered over a smaller extent, which mayprovide speckle reduction with relatively little reduction inresolution.

While the foregoing disclosure is directed to certain embodiments thatmay include certain specific elements, such embodiments and elements areshown as examples and various modifications thereto apparent to thoseskilled in the art may be made without departing from the conceptsdescribed and claimed herein. It is intended that all variations withinthe scope of the appended claims be embraced by the foregoingdisclosure.

What is claimed is:
 1. A projection display system, comprising: a lightsource for producing a beam of coherent light; a spatial light modulatorfor converting the beam of coherent light into individual image pixelswhich form an image at a display medium; a projection lens system; animage-displacement device, positioned between the modulator and at leasta portion of the projection lens system, for shifting the convertedlight beam to sequentially displace pixel positions of the image formedat the display medium by an amount, in a direction and at a frequencyfor optically dithering the formed images to reduce speckle; and whereinthe defined amount, direction and frequency shifts the converted lightbeam to displace the pixel positions by one pixel length or less.
 2. Thesystem of claim 1, wherein the image-displacement device is at least oneof a: (i) lens; (ii) mirror; (iii) transmissive element; (iv) platehaving parallel faces; and (v) optical element having non-parallelfaces.
 3. The system of claim 1, wherein the image-displacement devicedisplaces the pixel positions in a manner that is at least one of: (i)in a horizontal direction; (ii) in a vertical direction; (iii) at anangle; and (iv) at a frequency that is the same as that of an imageframe time.
 4. The system of claim 1, wherein the light source includesat least one of a: (i) solid-state laser diode; (ii) liquid laser; (iii)gas laser; (iv) light-emitting diode; (v) diode-pumped solid-statelaser: (vi) laser using direct emission diodes; and (vi)super-luminescent diodes.
 5. The system of claim 1, wherein the displaymedium is at least one of: (i) a surface having a diffusive property;and (ii) a surface having a scattering property.
 6. The system of claim1, wherein the image pixels form an image comprised of multiple rows andcolumns of pixels and the shifting displaces the pixel positions of theformed image in a direction aligned with the rows of the image.
 7. Thesystem of claim 1, wherein the image pixels form an image comprised ofmultiple rows and columns of pixels and the shifting displaces theformed image in a direction aligned with the columns of the image. 8.The system of claim 1, wherein the image-displacement device comprises amirror.
 9. The system of claim 1, wherein the defined amount, directionand frequency shifts the converted light beam to displace the pixelpositions by one pixel length or less so that each image is first formedas an original image at the display medium and then again formed as adisplaced image corresponding to the original image at the displaymedium within an image frame time.
 10. The system of claim 1, furthercomprising an actuator coupled for driving the image-displacement deviceto shift the converted light beam.
 11. The system of claim 10, whereinthe actuator is a piezoelectric element.
 12. The system of claim 10,further comprising a controller for providing signals to the actuatorthat control the driving of the image-displacement device.
 13. Thesystem of claim 12, wherein the controller defines an amount, directionand frequency for movement of the image-displacement device for a giventhrow ratio or distance between the image-displacement device anddisplay medium.
 14. The system of claim 1, wherein the defined amount,direction and frequency shifts the converted light beam to displace thepixel positions by at least one-quarter pixel length.
 15. The system ofclaim 14, wherein the controller defines the amount, direction andfrequency using a look-up table.